Cooled furnace and a cooling system therefor

ABSTRACT

A furnace over at least part of its outer surface is provided with a double wall, the space enclosed by said double wall being part of a circulation system for cooling liquid without pressure, there being a reservoir above the double wall space in which vaporized cooling liquid can be separated from the cooling mixture, which reservoir is in communication with the upper end and the lower end of the double wall space, the reservoir being in direct open communication with the upper end of the double wall space and being positioned immediately on top thereof and the double wall space being divided into two spaces by an intermediary baffle about parallel to the outer surface of the furnace, said two spaces being in open communication with each other at their upper and lower ends. The reservoir may extend from the upper end of the double wall space in upward and widening outward direction with respect to the furnace wall and may have at least one discharge duct for vapour connected thereto in the proximity of the highest and most outward area of this reservoir; may have in the proximity of the upper end of the double wall space, at the outside thereof, as part of the supply system for cooling liquid a liquid reservoir with an overflow which is connected to the space within the double wall through a narrow connecting passage; and may include other structural features.

United States Patent 1 Cramer et al.

[ 1 3,750,629 [451 Aug. 7, 1973 COOLED FURNACE AND A COOLING SYSTEM THEREFOR [75] Inventors: Rudolph E. Cramer, Beverwijk;

Cornelis Van Der Viliet, Akersloot;

Johannes H. W. Ouwerkerk, ljmuiden, all of Netherlands [73] Assignee: Koninklijke Nederlandsche Hoogovens En Staalfabrieken N.V., Ijmuiden, Netherlands 221 Filed: Oct. 20, 1971 21 Appl. No.: 190,745

' [30] Foreign Application Priority Data Oct. 23, 1970 Netherlands 7015595 June 14, 1971 Netherlands [52] U.S. Cl. 122/6 R, 266/32 [51] Int. Cl. F22b 37/00 [58] Field of Search 122/6 R, 7 R; 266/32 [56] References Cited UNITED STATES PATENTS 1,167,729 l/l9l6 Thornton 266/32 2,824,731 2/1958 Schwengel 266/32 3,212,476 10/1965 Markow et al 122/7 3,233,595 2/1966 De la Sauly et al. 122/7 Primary Examiner-Kenneth W. Sprague Att0rneyl-lall & Houghton [57] ABSTRACT A furnace over at least part of its outer surface is provided with a double wall, the space enclosed by said double wall being part of a circulation system for cooling liquid without pressure, there being a reservoir above the double wall space in which vaporized cooling liquid can be separated from the cooling mixture, which reservoir is in communication with the upper end and the lower end of the double wall space, the reservoir being in direct open communication with the upper end of the double wall space and being positioned immediately on top thereof and the double wall space being divided into two spaces by an intermediary baffle about parallel to the outer surface of the furnace, said two spaces being in open communication with each other at their upper and lower ends. The reservoir may extend from the upper end of the double wall space in upward and widening outward direction with respect to the furnace wall and may have at least one discharge duct for vapour connected thereto in the proximity of the highest and most outward area of this reservoir; may have in the proximity of the upper end of the double wall space, at the outside thereof, as part of the supply system for cooling liquid a liquid reservoir with an overflow which is connected to the space within the double wall through a narrow connecting passage; and may include other structural features.

19 Claims, 4 Drawing Figures PATENIED AUG 7 I973 SHEET 1 BF 3 PATENTEB AUG 7 I975 SHEET 2 BF 3 Fig. 4-

COOLED FURNACE AND A COOLING SYSTEM THEREFOR This invention relates to a furnace which along at least part of its outer surface is provided with a double wall, the space within said wall being part of a circulation system for cooling liquid, not under pressure, there being a reservoir above the double wall, in which vaporized cooling liquid can be separated from the cooling mixture, said reservoir being in communication with the upper and the lower end of the double wall space.

This invention also relates to a cooling system of the concerning type for the wall of a furnace.

When cooling the walls of furnaces, in particular of blast furnaces for making pig iron, use is sometimes made at present of so-called vaporization cooling. In particular if the refractory lining of the furnace is such that a uniform transmission of heat through said wall to the outside may be expected, this manner of cooling has advantages over the cooling of the furnace wall with the aid of cooling plates extending in the brick lining.

In such a vaporization cooling system a circulation is maintained so that in the double wall space part of the cooling liquid, usually water, is vaporized, and the vapour generated therefrom is allowed to escape from the open system. An equal quantity of cooling liquid is supplied into the reservoir for making up for such vapour losses.

An advantage of this manner of cooling consists in that in essence a very high quantity of heat can be discharged uniformly over a large surface area by the vaporization of the liquid. Another advantage consists in that this system is very well adapted to cause the cooling liquid to circulate through the system with simple means.

In known embodiments of vaporization cooling systems for furnaces the reservoir is positioned at some distance above the double wall space, and moreover there is a system of ducts between the upper end of the double wall space and the upper part of the reservoir, through which ducts the cooling fluid at least in part vapour is allowed to rise, and a system of ducts extending from the reservoir downwardly and opening into the lower part of the double wall space, through which cooling fluid is allowed to descend from the reservoir to the double wall space.

In the double wall space a mixture of liquid and vapour is formed, which mixture is conveyed by the ducts for the rising fluid to the reservoir. This mixture has a specific gravity which is several decades (tens) of percents lighter than the cooling liquid without vapour, which flows downwardly through the downflow ducts. It is from this difference in specific gravity that-the power is derived for keeping the cooling mixture circulating.

In order to have a force for this circulation which is of sufficient magnitude it is usual to position the reservoir at some distance above the double wall space, so that the total height of the double wall space plus the upflow ducts, or the total height of the downflow ducts respectively, is increased, so that as a result thereof also the difference in static pressure between the downflow ducts and the remainder of the circulating system is increased. 1

consists, however, in the fact that the vaporization within the double wall space often has the tendency to be quite irregular. Thereby it appears that the furnace wall runs the risk of being considerably superheated locally and temporarily. This will not only cause damage to the refractory lining and damage to the metal wall cladding, but it is even possible that there will be a break-through through the wall of the furnace as a result thereof.

In view of the above the invention is based upon the concept that it is possible that a film of vapour is generated over part of the wall in contact with the furnace and that the mentioned risks and dangers paritcularly occur if such a film is generated and exists during a somewhat longer period. Such vapour film becomes su-v perheated and particularly if this occurs it is a very good heat insulator between the furnace wall and the cooling liquid. Moreover the invention is based upon the concept that the generation of a coherent vapour film can be avoided by a suitable shape and embodiment of the circulation system.

In particular it appears that in the usual embodiment of the system of vaporization cooling the mixture of vapour and liquid flows through the upflow ducts quite irregularly and nonuniformly.

As a result thereof there occur considerable pressure shocks and it even appears that the through-flow of the mixture may temporarily be blocked fully, which can initiate the formation of a closed vapour film along the wall in contact with the furnace. Another disadvantage of the known vaporization cooling systems in furnaces consists in that the upflow ducts and the downflow ducts and also the auxiliary parts in such ducts as curves, valves etc., should be very wide in order to avoid that the resistance to flow in said ducts will become intolerably high. In particular it could be that such resistance to flow becomes greater than the contributionwhich the additional height of the upflow and downflow ducts gives to the motive force for circulating the cooling mixture. A large number of upflowand downflow ducts around the furnace could be of help, but this has considerable disadvantages because the furnace will be badly accessible thereby, in particular ,if such ducts have to be very wide. Often it is not even possible to have sufficient free space around the furnace to accommodate such ducts. The invention also aims at remedying such disadvantages.

In view of the above the invention consists in that, in a furnace with cooling means as described in the preamble, the vapour separating reservoir is in direct communication with the space within the double wall by being immediately positioned on top thereof and in open communication therewith and that the double wall space is divided into two spaces by an intermediary baffle means being about parallel to the outer surface of the furnace, said two spaces to both sides of the baffle being in open communication with each other at the upper and lower end of the double wall space.

As it is thereby possible that the separation of vapour and cooling liquid takes place in the close proximity of the upper end of the double wall space, there is no danger of an irregular flow of the mixture of two phases, liquid and vapour, after leaving the double wall space. The'occurrence of pressure shocks in the circulation system is, as hasappeared, avoided thereby, so that it is neither possible that a coherent film of vapour is formed in contact with the wall which is in contact with the furnace. On the contrary vapour bubbles will form uniformly distributed over the double wall space, said bubbles being rapidly torn away from said wall and entrained by the flow of liquid. Over the entire height of the double wall space in the inner space thereof there will form a mixture of two phases uniformly distributed and flowing regularly and uniformly to the reservoir.

As no separate upflow and downflow ducts are necessary a much more simple and cheap structure is obtained. which moreover makes the furnace 'much more readily accessible.

It is remarked that the outer space of the double wall space in fact acts as a downflow duct. By the absence of additional upflow and downflow ducts the height of rising and falling of the circulating cooling mixture is decreased, so that one could fear that there would be insufficient circulation. It has, however, surprisingly appeared that the occurring circulation is amply sufficient for the purpose, which probably should be ascribed to the fact that the additional resistance of flow for the liquid in the known upflow and downflow ducts is no longer encountered. Moreover it appears that the more uniform circulation through the new circulation system considerably promotes the uniform cooling.

- It has appeared that the vapour separating reservoir may have quite limited dimensions. On the other hand it is preferred to give to this reservoir a shape in which the upper end of the double wall extends both upwardly and outwardly with respect to the furnace, there being at least one vapour discharge duct connected to the highest and most outward zone of this reservoir. On the one hand this gives thatthe furnace wall above the double wall is well accessible for eg, the provision of other cooling systems, on the other hand it is in this way avoided that liquid enters the vapour discharge duct and thus disturbs the uniform discharge of vapour.

When supplying liquid for compensating the loss of vapour discharged several systems are possible. It is possible to meter into the lower end of the circulation system a quantity of liquid which is constant per unit time. However, it appears necessary to make the quantity of supplied liquid dependent upon the quantity of vapour discharged as otherwise there is the danger that the liquid level in the circulation system becomestoo high or too low to an extent which is not permissible. A control system in whichthe liquid supply is controlled depending upon the measured quantity of vapour discharged appears to be unnecessarily complicated and moreover this does not insure a good operation of the system. Moreover, it has appeared that when introducing cold liquid into the lower end of the circulation system difiiculties may arise. In particular this retards the formation of vapour in the lower part of the inner space of the double wall in contact with the furnace, which decreases the capacity of the cooling system.

It is possible to avoid such disadvantages if according to the invention the furnace is embodied in such a way that in the proximity of the upper end of the double wall space a supply system "for cooling liquid is connected thereto, which includes a reservoir with. an overflow and which is connected through at the outside thereof a cooling liquid narrow connecting passage to the space within thc'double wall.

As said supply system is arranged close to the upper end of the double wall space, it is possible for the liquid supplied to be preheated during moving thereof towards the lower end of the double wall space, such heating being possible even to close to the boiling point, so that the forming of vapour may begin substantially at the lower end of the double wall space. Due to the narrow connecting passage between the reservoir with the overflow and the outer space within the double wali it is avoided that pressure vairations within said double wall space as a result of the boiling phenomenon extend their influence considerably into said reservoir with the overflow. By positioning the overflow at a height which corresponds to the average desired liquid level in the outer space of the double wall space a reliable selfcontrolling supply of liquid is obtained.

The separation of vapour and liquid can be considerablyimproved ifin the reservoir an additional provision according to the invention is made, consisting in that in the reservoir a splash baffle is provided, which extends from the inner wall, as seen from the centre of the furnace, in an inclined upward direction outwardly to above and past the inner space, as seen from the centre of the furnace, and thereafter is bent gradually downwards so as to terminate freely in the reservoir.

The mixture of vapour and liquid rising at high speed in the space is diverted by said splash baffle, the liquid droplets being projected back into the outer space. It has appeared that in this way only very little liquid enters the discharge duct forthe vapour and that the level of the liquid in the outer space is much more quiet thanks to this provision. It is also possible thereby to obtain the supplementing of the cooling liquid in a more favourable way. To this end according to the invention at least one supply duct for cooling liquid opens into the upper wall of the reservoir above the upwardly directed splash baffle. This liquid thus fills the space between the furnace wall and the inclined splash baffle and from there flows over said baffle into the outer space of the double wall space. Such an intermediary storing of cooling liquid gives several advantages. Thus the upper part of the furnace wall within the reservoir and the splash baffle are cooled additionally. Moreover a preheating of the supplied liquid takes place before it enters the outer space. In this case it is preferred to provide a measuring reservoir for measuring the level of the cooling liquid near the upper end of the double wall space, which reservoir is connected through a narrow connecting passage to the space within the double wall, and that a control system is'present, by which the supply of additional cooling liquid is controlled depending on a signal derived from the measuring of the level as stated.

If the furnace wall is under heavy thermal load it may be advantageous according to the invention to provide means for heating the supplementing cooling liquid to the proximity of the boiling temperature upstream of the opening of the suppletion system for this supplementing liquid into the circulation system. Thereby the certainty is obtained that the cooling liquid will begin to boil immediately in the lower part of the inner space of the double wallspace and that thereby cooling by vaporization takes place over the maximum length along the height of the cooling system.

Of course it would be possible to control the liquid supply proportionally to a continuously measured variation in level in the measuring reservoir. It has, however, appeared that it is sufficiently satisfactory for operation to have a system in which in the measuring res- I ervoir a maximum-minimum-level-switch is arranged, with the aid of which the supply of additional cooling liquid can be switched on between two extremes. An advantage obtained with such a control consists in that no liquid is unnecessarily lost over an overflow. Particularly if demineralized water is used as a cooling liquid, this gives a considerable saving in costs.

The flow of liquid in the circulation system moreover appears to be open to improvement obtained if according to the invention the spaces within the double wall are moreover also subdivided by a set of vertical baffles into parallel passages, said vertical baffles extending substantially perpendicularly to the furnace wall to be cooled. Thereby the interaction in cooling of different parts of the furnace is decreased while moreover it is avoided that in the double wall space by transverse flows preferred flow paths occur. In this respect it is, however, necessary to take care that the intermediary baffle means extending substantially peripheral to the furnace wall to be cooled extends to above the upper edge of such set of baffles extending perpendicularly to said furnace wall and that all these latter baffles always are submerged below the liquid level.

In particular the proposed structure has appeared to be advantageous if it is applied to ablast furnace in which the double wall encloses the bosh of the blast furnace. The cooling of the bosh in this way in particular gives advantages because, as the shape of the bosh is conical and wider above than below a good contact of the masonry of this part of the furnace with the double wall as a result of the own weight of this masonry does not give a problem.

For the good operation of the system it is necessary that particular care is given to the choice of the dimensions thereof. This choice should be directed to the requirement that in the top part of the inner space of the double wall the mixture of liquid and vapour consists for at most about 50 percent by volume of vapour.

Of course such a situation is only realizable with a certain circulation of the cooling mixture as'a result of a special dimensioning of the circulation system. It has appeared that good results are possible if according to the invention the widths of the spaces of the double wall, the inner and the outer space respectively, as seen in a direction perpendicular to the furnace wall, have a mutual ratio of 1.5 to I up to 2.5 to land preferably about 2 to 1 and that the sum of these widths at the upper end of the double wall is about twice this sum at the lower end thereof. In particular good results are obtained if the inner space, as seen perpendicularly to the furnace wall, has a width which is about cm at the lower end and goes to about cm at the upper end.

Although the invention has been described with particular reference to a blast furnace it is'as well applicable to cooling systems for cooling furnaces of other types. In particular the invention has appeared to be of high value if applied to a tunnel furnace. In this case two mutually separated circulation systems for cooling liquid of the given kind are arranged along at least part of the cooling zone of this tunnel furnace. Such cooling systems may each consist of a series of several mutually separated cooling elements, but it is also possible that each circulation system consists of one single cooling element of the type above described. In particular it has, when applying the invention to a tunnel furnace, appeared advantageous to have the inner wall of the double wall, which inner wall forms the outer wall of part of the furnace, be in contact with a gas space along the side wall of the furnace, separated from the space through which the products pass through the tunnel furnace by a wall, which leaves a connection between said spaces at top and bottom for allowing a gas circulation through said gas space.

The invention will now be explained in more detail with reference to several Figures of the enclosed drawings giving diagrammatically two possible embodiments of systems according to the invention. I

FIG. 1 diagrammatically shows a blast furnace with a cooling system according to the invention.

FIG. 2 shows detail II of FIG. I at an enlarged scale.

FIG. 3 shows-another embodiment of this detail.

FIG. 4 shows the application of the invention to a tunnel furnace.

FIG. 1 shows a vertical section and part upright view of a blast furnace I in a diagrammatic way.

Around the bosh 2 of the furnace a cooling system according to the invention is arranged, which in FIG. 1 is shown only in part and diagrammatically. This cooling system essentially consists of a double wall which in peripheral direction of the furnace is built up of several sections. Reference numerals 3 and 4 indicate two of said sections shown diagrammatically. At the upper end of the double wall space vapour discharge ducts are connected thereto, two of them being shown and indicated by reference numerals 5 and 6. At 7-and 8 additional cooling liquid for suppletion may be supplied'to the cooling system. In the further description the cooling liquid is supposed to be water, whichis the most usual liquid to use.

In FIG. 1 the several elements are for sake of clarity not shown in their real mutual proportion, the radial dimensions of the cooling sections being of course much smaller than shown.

In FIG. 2 detail II of FIG. I is given at an enlarged scale. It is clear therefrom that in the double wall space 3 an intermediary baffle 9 is positioned, extending in peripheral direction. This baffle 9 extends tothe proximity of the upper end and the lower end of the double wall' space and divides said space into two spaces namely, liquid and vapour upflow and liquid downflow spaces 10 and 11. At the upper end the double wall 3 is closed by vapour separating reservoir 28 which extends in an upward and radially outward direction. At the highest point of said reservoir a steam discharge duct 5 is connected.

. At several points around the furnace reservoirs 13 are positioned in the proximity of the upper end of the space 11. Said reservoirs 13 have an overflow weir and During operation of the furnace it appears that in the double wall space there is sufficient circulation to cool the enclosed part of the-furnace effectively. There appears to be a regular and uniform formation of steam in space 10, without local superheating of the wall. The vapour generated is separated in reservoir 28 from the cooling mixture and water which is substantially free from steam descends through the space 11. By the difference in specific gravity between the mixture of water and steam in space 10 and the vapourfree water in space I] a sufficient natural circulation or syphon action is obtained.

Although it is possible to cool the water vapour escaping through duct 5 by means of a coolerand to feed it back as water into the system, it is for structural reasons preferred to let the steam escape and to replace it by fresh water from reservoir 13.

The narrow connection 12 between this reservoir 13 and space 11 assures in the form of FIG. 2 a calm and uniform flow of water from the reservoir into the circulation system without too much disturbance.

In FIG. 3 another embodiment of the same detail has been shown. in this case a splash baffle 14 is arranged, which projects the water entrained by the steam back into the water in space 11. On the splash baffle 14 suppletion water 15 is present, which is supplied by duct iii. In a representative situation of operation a supply of one tenth of a percent of the circulating water quan' tity has appeared necessary. in a measuring reservoir 17 which through duct 18 is in connection with space II, the level of the water in reservoir 28 is measured. When reaching the levels 19 and 20 respectively the supply of water through duct i6 is decreased and increased respectively. The control system necessary thereto has not been shown in detail as this is simple and will be clear to the expert. An overflow 21 has been arranged for unforeseen circumstances. Space 10 widens from below to above from a width of about l0 cm to 20 cm and space 11 widens upwardly from about 5 cm to ID cm measured at the bend shown'at 22 in the outer wall, where'this outerwall merges into part 23 thereof, forming the wall of the reservoir 28.

In FIG. 4 an application of the invention is shown for a tunnel furnace and this is'also shown diagrammatically. Only a symmetrical half of a cross-section of this tunnel furnace is shown here. Therein reference numerals 31 and 32 show the bottom and the roof of this furnace respectively. In a side wall 33openings 34 and 35 are applied at the upper and lower end respectively. Said openings communicate with a gas space 36 outside the partition wall 33, through which space the gas from the tunnel in the furnace is circulated, e.g. by natural circulation or'syphon action. Space 36 at the outside is limited by a series of cooling elements which together form a cooling system according to the invention. Each of said cooling elements comprises an inner wall 37, an

intermediary baffle 38 and an outer wall 39. Upwardly the cooling element widens over about the upper half thereof. A splash baffle 40 is provided at the upper end of the cooling element for deflecting and returning the mixture of rising vapour and liquid. in other respects this cooling system is embodied essentially in the same way as the cooling system according to FIGS. 2 and 3. The evaporated water can escape as vapour through opening 41, the system being supplemented with water to make up for this escape through opening 42. In this case, contrary to the previous embodiments, it is preferred to cool the vapour escaping through duct 41 to condense it and to feed it back into the system in a manner which is known as such.

The cooling elements described are only arranged 6 tained, which moreover is highly reliable. This is particularly of importance if in the tunnel furnace ceramic products are baked, of which the cooling should take place rapidly and in a very accurately controlled manner. An additional advantage of the described manner of cooling is that the cooling elements can be replaced simply and rapidly without causing a long time interruption of the operation of the furnace.

We claim:

1. An improved vaporization cooled furnace, said furnace being of the type comprising:

a. acirculating system for cooling liquid, said system comprising 1. a double walled portion extending over at least a part of the outer surface of the furnace, and defining a circulating space for said liquid,

2. a vapor separating reservoir above said double walled portion, and in communication with the upper and lower ends of said space, and

b. vapor venting means in communication with said vapor separating reservoir, said furnace being improved in that c. said vapor separating reservoir is positioned immediately on top of said double walled space and has a direct open communication with the upper end of said space,

v d. said system further comprises baffle means in said I space below said vapor separating reservoir, and about parallel tothe outer surface of the furnace, which baffle means divides said space into inner liquid and vapor upflow and outer liquid downflow 's sees in open communication with each other at t eir upper and lower ends, and

c. said system further comprises means for establishing a liquid level in said outer downflow space in proximity to the upper end of said baffle means and below said vapor separating reservoir.

2. A furnace as claimed in claim 1 wherein:

i. said vapor separating reservoir extends from the upper end of said double walled space and widens upwardly and outwardly with respect to the furnace wall, and

g. said vapor venting means comprises at least one vapor discharge duct connected to said vapor separating reservoir in proximity to the highest and most outwardly extending portion thereof.

3. A furnace as claimed in claim 1 wherein:

f. said liquid level establishing means comprises, in proximity to the upper end of said downflow space, a cooling liquid reservoir having an overflow therefrom, and

g. a narrow passage connecting said liquid reservoir to said liquid downflow space.

4. A furnace as claimed inclaim 3, wherein said narrow passage is connected to said liquid downflow space near the upper end thereof.

5. A furnace as claimed in claim 1, wherein:

f. said means for establishing a liquid level in said downflow space comprises means for supplying liquid to said circulating system and means for heating to approximately its boiling point the liquid being so supplied prior to the delivery thereof into said upflow space.

6. A furnace as claimed in claim 1, further comprisi. a splash baffle in said vapor separating reservoir, said splash baffle extending, from the inner wall of the double walled space, outwardly in an upwardly inclined direction above and past said upflow space and curving downwardly above said downflow space and terminating freely thereabove.

7. A furnace as claimed in claim 6, wherein:

g. said means for establishing a liquid level in said downflow space comprises means for supplying cooling liquid opening into said vapor separating reservoir above said upwardly directed splash baffle to flow across said splash baffle into said liquid downflow space. i

8. A furnace as claimed in claim 7, wherein:

h. said means for establishing a liquid level in said downflow space further comprises, in proximity to the upper end of said down-flow space, a cooling liquid reservoir,

i. a narrowpassage connecting said cooling liquid reservoir to said downflow space, and

j. means for controlling said cooling liquid supplying means in dependence on the liquid level in said liquid reservoir.

9. A furnace as claimed in claim 8, wherein said controlling means comprises a switching means in said liquid reservoir operated at maximum and minimum levels of liquid therein for controlling said liquid supplying means.

10. A furnace as claimed in claim 1, wherein said system further comprises:

f. a set of baffles positioned substantially vertically and extending into said upflow space in a direction from the inside of the furnace toward the outside thereof.

11. A furnace as claimed in claim 10, wherein said baffle means extends upwardly to a higher level than said set of baffles.

12. A furnace as claimed in claim 1, wherein:

f. the widths of said inner upflow and outer downflow spaces are proportioned in the range of from 1.5 to 1 up to 2.5 to 1, and

g. the sum of said widths at the upper end of said baffle means is about twice the sum of said widths at the lower end thereof.

13. A furnace as claimed in claim 12, wherein:

h. the width of said inner upflow space is about 10 centimeters at the lower end of said baffle means and gradually increases to about centimeters at the upper end of said baffle means.

14. An improved vaporization cooling system for a furnace, said cooling system comprising: i i

a. a double walled portion for extending over at least a part of the outer surface of the furnace and defin ing a circulating space for said liquid,

b. a vapor separating reservoir above said double walled portion, and in communication with the upper and lower ends of said space, and vapor venting means in communication with said vapor separating reservoir, said cooling system being improved in that said vapor separating reservoir is positioned immediately on top of said double walled space and has a direct open communication with the upper end of said space,

d. said system further comprises baffle means in said space below siad vapor separating reservoir positioned to lie about parallel to the outer surface of the furnace, which baffle means divides said space into inner liquid and vapor upflow and outer liquid downflow spaces in open communication with each other at their upper and lower ends, and

e. said system further comprises means for establishing a liquid level in said outer downflow space in proximity to the upper end of said baffle means and below said vapor separating reservoir.

15. A cooling system as claimed in claim 14, particularly adapted for cooling the wall of a vertical shaft furnace, and comprising a series of separate units formed to abut one another and extend around part of the wall of such furnace.

16. A cooling system as claimed in claim 14, particu' larly adapted for cooling opposite vertical walls of a tunnel furnace, and comprising two-series of separate units formed to extend along the two opposite walls of the tunnel furnace, respectively.

17. A cooling system according to claim 16, said two series each comprising at least one of said units.

18. A cooling system as claimed in claim 17, said two series each comprising a plurality of said units in mutually abutting relation.

19. A cooling system as claimed in claim 16, and in combination therewith a tunnel furnace, the inner wall of the double walled portion of said cooling system forming the outer wall of part of said furnace, said furnace having a gas space therein adjacent said wall, and also having a partition wall separating said gas space from the tunnel of the furnace, said partition wall having passage means at its top and bottom portions providing for circulation of gas from said tunnel through said gas space. 

1. An improved vaporization cooled furnace, said furnace being of the type comprising: a. a circulating system for cooling liquid, said system comprising
 1. a double walled portion extending over at least a part of the outer surface of the furnace, and defining a circulating space for said liquid,
 2. a vapor separating reservoir above said double walled portion, and in communication with the upper and lower ends of said space, and b. vapor venting means in communication with said vapor separating reservoir, said furnace being improved in that c. said vapor separating reservoir is positioned immediately on top of said double walled space and has a direct open communication with the upper end of said space, d. said system further comprises baffle means in said space below said vapor separating reservoir, and about parallel to the outer surface of the furnace, which baffle means divides said space into inner liquid and vapor upfloW and outer liquid downflow spaces in open communication with each other at their upper and lower ends, and e. said system further comprises means for establishing a liquid level in said outer downflow space in proximity to the upper end of said baffle means and below said vapor separating reservoir.
 2. A furnace as claimed in claim 1 wherein: f. said vapor separating reservoir extends from the upper end of said double walled space and widens upwardly and outwardly with respect to the furnace wall, and g. said vapor venting means comprises at least one vapor discharge duct connected to said vapor separating reservoir in proximity to the highest and most outwardly extending portion thereof.
 2. a vapor separating reservoir above said double walled portion, and in communication with the upper and lower ends of said space, and b. vapor venting means in communication with said vapor separating reservoir, said furnace being improved in that c. said vapor separating reservoir is positioned immediately on top of said double walled space and has a direct open communication with the upper end of said space, d. said system further comprises baffle means in said space below said vapor separating reservoir, and about parallel to the outer surface of the furnace, which baffle means divides said space into inner liquid and vapor upfloW and outer liquid downflow spaces in open communication with each other at their upper and lower ends, and e. said system further comprises means for establishing a liquid level in said outer downflow space in proximity to the upper end of said baffle means and below said vapor separating reservoir.
 3. A furnace as claimed in claim 1 wherein: f. said liquid level establishing means comprises, in proximity to the upper end of said downflow space, a cooling liquid reservoir having an overflow therefrom, and g. a narrow passage connecting said liquid reservoir to said liquid downflow space.
 4. A furnace as claimed in claim 3, wherein said narrow passage is connected to said liquid downflow space near the upper end thereof.
 5. A furnace as claimed in claim 1, wherein: f. said means for establishing a liquid level in said downflow space comprises means for supplying liquid to said circulating system and means for heating to approximately its boiling point the liquid being so supplied prior to the delivery thereof into said upflow space.
 6. A furnace as claimed in claim 1, further comprising: f. a splash baffle in said vapor separating reservoir, said splash baffle extending, from the inner wall of the double walled space, outwardly in an upwardly inclined direction above and past said upflow space and curving downwardly above said downflow space and terminating freely thereabove.
 7. A furnace as claimed in claim 6, wherein: g. said means for establishing a liquid level in said downflow space comprises means for supplying cooling liquid opening into said vapor separating reservoir above said upwardly directed splash baffle to flow across said splash baffle into said liquid downflow space.
 8. A furnace as claimed in claim 7, wherein: h. said means for establishing a liquid level in said downflow space further comprises, in proximity to the upper end of said downflow space, a cooling liquid reservoir, i. a narrow passage connecting said cooling liquid reservoir to said downflow space, and j. means for controlling said cooling liquid supplying means in dependence on the liquid level in said liquid reservoir.
 9. A furnace as claimed in claim 8, wherein said controlling means comprises a switching means in said liquid reservoir operated at maximum and minimum levels of liquid therein for controlling said liquid supplying means.
 10. A furnace as claimed in claim 1, wherein said system further comprises: f. a set of baffles positioned substantially vertically and extending into said upflow space in a direction from the inside of the furnace toward the outside thereof.
 11. A furnace as claimed in claim 10, wherein said baffle means extends upwardly to a higher level than said set of baffles.
 12. A furnace as claimed in claim 1, wherein: f. the widths of said inner upflow and outer downflow spaces are proportioned in the range of from 1.5 to 1 up to 2.5 to 1, and g. the sum of said widths at the upper end of said baffle means is about twice the sum of said widths at the lower end thereof.
 13. A furnace as claimed in claim 12, wherein: h. the width of said inner upflow space is about 10 centimeters at the lower end of said baffle means and gradually increases to about 20 centimeters at the upper end of said baffle means.
 14. An improved vaporization cooling system for a furnace, said cooling system comprising: a. a double walled portion for extending over at least a part of the outer surface of the furnace and defining a circulating space for said Liquid, b. a vapor separating reservoir above said double walled portion, and in communication with the upper and lower ends of said space, and vapor venting means in communication with said vapor separating reservoir, said cooling system being improved in that c. said vapor separating reservoir is positioned immediately on top of said double walled space and has a direct open communication with the upper end of said space, d. said system further comprises baffle means in said space below said vapor separating reservoir positioned to lie about parallel to the outer surface of the furnace, which baffle means divides said space into inner liquid and vapor upflow and outer liquid downflow spaces in open communication with each other at their upper and lower ends, and e. said system further comprises means for establishing a liquid level in said outer downflow space in proximity to the upper end of said baffle means and below said vapor separating reservoir.
 15. A cooling system as claimed in claim 14, particularly adapted for cooling the wall of a vertical shaft furnace, and comprising a series of separate units formed to abut one another and extend around part of the wall of such furnace.
 16. A cooling system as claimed in claim 14, particularly adapted for cooling opposite vertical walls of a tunnel furnace, and comprising two series of separate units formed to extend along the two opposite walls of the tunnel furnace, respectively.
 17. A cooling system according to claim 16, said two series each comprising at least one of said units.
 18. A cooling system as claimed in claim 17, said two series each comprising a plurality of said units in mutually abutting relation.
 19. A cooling system as claimed in claim 16, and in combination therewith a tunnel furnace, the inner wall of the double walled portion of said cooling system forming the outer wall of part of said furnace, said furnace having a gas space therein adjacent said wall, and also having a partition wall separating said gas space from the tunnel of the furnace, said partition wall having passage means at its top and bottom portions providing for circulation of gas from said tunnel through said gas space. 